It is frequently desirable to take biopsy samples from a patient. In bone marrow biopsy, it is always necessary to puncture the bone of a patient in order to retrieve bone marrow which normally exists only in the center of a bone.
It may be desirable to retrieve bone marrow for several different reasons. In one type of bone marrow procedure, it is desirable to retrieve a "core" of bone marrow to examine bone marrow architecture. This procedure may be useful in determining whether a patient has cancer and the extent of cancerous cells that may exist. Examining a bone marrow core typically involves an extended period of time in which the core is first prepared and then sliced into thin samples which are examined under a microscope.
In other bone marrow procedures, it is desirable to simply aspirate cells of the bone marrow to make a relatively rapid examination to indicate the state of a patient's disease and to aid in the diagnosis of a patient.
Finally, in other bone marrow procedures, multiple aspirations of bone marrow are conducted to perform a bone marrow transplant. While each of these procedures has different goals, they all require that the bone be punctured in order to access the bone marrow within. Thus, it is important to provide a needle which enhances the ability of the user to puncture bone with minimal trauma to the patient.
All bone marrow biopsy, aspiration and transplant needles currently on the market have a handle with a cannula extending outwardly from the handle. The handle is used by the doctor to apply force to the cannula as the cannula penetrates the bone. Such needles typically include a stylet with a sharpened tip which is inserted through the cannula and is used to initially penetrate the bone. The stylet also serves to occlude the cannula while the bone is penetrated, so that the marrow sample subsequently taken is free from bone chips. The stylet is then removed and bone marrow is withdrawn from the patient by manipulating the cannula to cause bone marrow to move into the interior of the cannula. In some cases a slight suction is applied to the cannula to hold the bone marrow specimen within the cannula as the device is removed from the patient.
Bone marrow needles have traditionally been designed so that the needle is attached to the center of the handle. While many physicians feel comfortable with a centrally attached needle, it has now been discovered that it may be easier to guide a needle with a user's index finger when the needle is not centrally located on the handle of the needle assembly. It has also recently been discovered that when an off-center device is used, it is important to insure that a physician's arm, wrist, and index finger are all generally in alignment with the cannula of the needle to provide enhanced control over the needle. Examples of such devices are described in U.S. Pat. Nos. 4,469,109 and 4,838,282.
A disadvantage of most bone marrow needle assemblies currently on the market is that when the stylet is removed from the cannula, the shape of the handle typically is materially changed. For example, the bone marrow needle assembly described in U.S. Pat. No. 4,838,282 involves removing approximately half of the handle assembly when the stylet is removed from the cannula. It has recently been discovered, as part of the subject invention, that it is desirable to maintain the original shape of the handle after the stylet has been removed to allow a physician to more easily manipulate the cannula within a patient's bone.